Chimps kill, wage war to gain territory: study

WASHINGTON — Chimpanzees wage war, mercilessly killing members of neighbouring groups to expand their own territory, researchers reported on Monday.

While biologists had long suspected that chimp violence could be more than random, the study in Current Biology provides the first clear evidence of this.

“Although some previous observations appear to support that hypothesis, until now, we have lacked clear-cut evidence,” University of Michigan primate behavioral ecologist John Mitani said in a statement. The researchers spent 10 years watching two groups of chimpanzees living in Ngogo in Uganda’s Kibale National Park. One was unusually large, with about 150 members, and appeared to have a disproportionate number of males.

“During this time, we observed the Ngogo chimpanzees kill or fatally wound 18 individuals from other groups,” the researchers wrote. They saw evidence of three more killings.

They noticed unusual chimpanzee patrols in which the animals moved quickly, silently and in single file, carefully watching for other chimpanzees.

Anthropologist Sylvia Amsler, now at at the University of Arkansas at Little Rock, was a graduate student working with Mitani when she saw one such patrol launch an attack.

“They had been on patrol outside of their territory for more than two hours when they surprised a small group of females from the community to the northwest,” Ms. Amsler said in a statement. “Almost immediately upon making contact, the adult males in the patrol party began attacking the unknown females, two of whom were carrying dependent infants.”

The attackers quickly killed one and struggled with the mother of the second over a period of an hour and a half.

“Though they were never successful in grabbing the infant from its mother, the infant was obviously very badly injured, and we don’t believe it could have survived,” Ms. Amsler said.

Soon after the killings, the researchers noticed that the Ngogo chimpanzees expanded their territory considerably — by more than 22%.

“When they started to move into this area, it didn’t take much time to realize that they had killed a lot of other chimpanzees there,” Mr. Mitani said.

While chimpanzees are the closest living relatives of human beings, Mr. Mitani is unsure if the warlike behavior sheds light on human warfare. “Warfare in the human sense occurs for lots of different reasons,” he said. “I’m just not convinced we’re talking about the same thing.”

What the behavior may point to is co-operation.

“The lethal intergroup aggression that we have witnessed is cooperative in nature, insofar as it involves coalitions of males attacking others. In the process, our chimpanzees have acquired more land and resources that are then redistributed to others in the group.”

The area was remote and no people lived around there, so the researchers reject the theory that pressure from humans may have caused unusual behavior among the chimpanzees.